Particle tracking bugs

Tracking Monte Carlo particles (or in this case, ray traces) through a geometry can be tricky because of the subtlety of edge cases. Today I discovered that my tracking routine failed when given a direction of −0.0 . I never imagined that the existence of signed zeroes in IEEE floating point arithmetic could ever bite me.

Starting Terminal.app with multiple tabs in multiple directories

Almost every time I open up Terminal, I've wanted three tabs open with three particular directories. That means using Cmd-Tab a lot and tab completion to change the directory. I finally got fed up with that and invented a solution to take care of that automatically.

The first step is creating a "Window group" in the terminal. Go to the menu item "Windows < Save Windows as Group…", make up a name, and make sure "use this group at startup" is checked.

The second step is to edit your ~/.bash_profile and add something like this, where each "if" statement gets a different command. This is adaptable to changing the base directory, sshing, etc.

# change PWD to python by default
function change_default_directory() {
 TTYN=$(tty | sed -e 's/.*ttys\([0-9]*\)/\1/')
 if [[ $TTYN == 000  ]]; then
  cd ~/_code/pytrt/
 elif [[ $TTYN == 001  ]]; then
  cd ~/_code/_build/pytrt/
 elif [[ $TTYN == 002  ]]; then
  cd ~/_code/_build/pytrtDEBUG/
 elif [[ $TTYN == 003  ]]; then
  cd ~/_research/current/
 fi
}

if [ -n "$PS1" ]; then
 change_default_directory;
fi

Add more elif blocks if you open five windows, take away more if you open fewer. Enjoy!

Reflecting on the hard work I've put into my research code

I am still proud of my code to get the angle in a quadrature set reflected across an axis. It's a little crazy.

const AngleT& getReflectedAngle(const AngleT& a, unsigned int axis ) const {
    return angles_[ (a.getOctantIndex() ^ (1 + ( axis << 1)) + 1) * numAnglesPerOctant_ - 1 - a.getSubIndex() ];
}

This section of code is copyright © 2011 Seth R Johnson, All rights reserved.